Conventional air-curing tobacco barns utilize natural convection, with air flow generally proceeding from the bottom of the barn toward the top of the barn. In curing tobacco by the procedure generally referred to as the “bulk curing” method, tobacco leaves are loaded in a relatively compact mass on racks or in containers and placed inside of an enclosed curing barn where a furnace or a plurality of heaters circulate a forced flow of heated air through the mass of tobacco leaves to effect curing and drying. Conventional tobacco curing barns attempt to obtain the desired atmospheric conditions such as temperature and humidity within the tobacco barn by various adjustments of louvers or openings in the sides of the barn and the operation of heaters spaced along the floor of the barn with respect to the prevailing temperature and moisture content of the outside atmosphere, the wind velocity and its direction with respect to the tobacco barn. A number of problems have been observed when curing tobacco in conventional air-curing barns. The different tiers of tobacco stacked in the barn cure at different rates, the tips of the tobacco leaves are often found to dry too quickly, during dry ambient weather, the tobacco may dry too quickly and have poor quality, and during humid ambient weather the tobacco may rot and have poor quality along with elevated contents of tobacco specific nitrosamines.